Beam splitters are some of the basic optical elements and are used in various optical assemblies for spatial beam shaping. A typical beam splitter is used to divide a single optical beam into two beams to propagate along different optical paths.
Beam splitters are typically used to separate collected illumination between multiple light detection channels associated with multiple detectors, as well as spatially separating illumination and detection channels. Multiple detectors might be useful in scanning optical microscopy. The latter is typically based on inspecting/imaging a sample by illuminating successive regions on the sample, using one or more illuminating spots. It is often the case that such scanning optics is used with an array of detectors, rather than using a single movable detector.